Laterally folding wheelchairs have been in use for over fifty years and many models are still on the market. There are two general systems to accomplish lateral, as opposed to longitudinal, folding. In the sliding tube system, cross members in an X-configuration are articulated, at the lower ends, to the lower side frame rails and, at the upper ends, to the seat rail. The cross members include a telescopically sliding tube so that on folding the side frames are held in alignment with the seat rails. When the seat rails are raised, the system collapses and the seat rails rise relative to the side frame.
Most contemporary wheelchairs, however, incorporate a link system to conserve weight and provide a more stable frame system than is possible with the sliding tube system. The X-frames are essentially the same in that they are articulated to the side rails and seat rails. However, when the chair is in the open position the seat rail rests in a saddle which is attached to the side frame. A link which articulates with the upper side member rail and the cross member is used to maintain alignment during folding. The link system is folded and unfolded in the same manner as the sliding tube system and the seat rail rises relative to the side frame when folded. Unfortunately neither of these two lateral folding systems can be used with a chair which incorporates a tilt function. Wheelchairs which incorporate a tilt function have heretofore always been of the longitudinal folding type which are not as convenient or as compact and hence not favored in the market. As used herein the term tilt means the function which allows the seat and back of the chair to change angle as a unit relative to the horizontal, in contrast to a reclining chair in which the back angle is changed relative to the position of the seat.